CN110919026A

CN110919026A - Sn @ Ti3C2Battery cathode material and preparation method thereof

Info

Publication number: CN110919026A
Application number: CN201911254599.0A
Authority: CN
Inventors: 柏寄荣; 王志磊; 许�鹏; 刘天宇; 周全法
Original assignee: Changzhou Institute of Technology
Current assignee: Changzhou Institute of Technology
Priority date: 2019-12-10
Filing date: 2019-12-10
Publication date: 2020-03-27

Abstract

The invention discloses Sn @ Ti₃C₂A battery cathode material and a preparation method thereof belong to the technical field of lithium batteries. The invention etches Ti by LiF and HCl₃AlC₂Medium Al layer to obtain Ti₃C₂MXene nanosheets utilizing NaBH₄Reducing the solution to obtain Sn nanoparticlesWith Ti₃C₂Mixing and stirring MXene colloidal solution for reaction to finally obtain Sn @ Ti of three-dimensional superstructure₃C₂. Sn @ Ti prepared by the invention₃C₂Specific Surface Area (SSA) value of 14.868m of battery negative electrode material²G, with Ti₃C₂Compared with MXene, Sn @ Ti in layer-by-layer superstructure₃C₂The specific surface area of the Sn @ Ti is obviously increased, and simultaneously the Sn @ Ti prepared by the invention₃C₂Has good stability and excellent electrochemical reversibility, and after 100 cycles, the Sn @ Ti₃C₂The specific capacity of the catalyst can still be maintained at 702.38mA h g^‑1。

Description

Sn @ Ti3C2Battery cathode material and preparation method thereof

Technical Field

The invention relates to Sn @ Ti₃C₂A battery cathode material and a preparation method thereof belong to the technical field of lithium batteries.

Background

Currently, with the rapid development of portable electronic products and the wide application of smart grids, electrochemical materials having high energy density are receiving wide attention. Among them, Lithium Ion Batteries (LIBs) have advantages of high energy density, environmental protection and long cycle life, and are dominant in the battery market. However, the commercial graphite anode material has a low theoretical capacity, so that it is difficult to satisfy practical requirements.

The rapid development of two-dimensional (2D) materials provides a good opportunity for the construction of high performance LIBs. 2D materials with larger specific surface area will generate more active sites than 0D or 1D materials; in addition, the in-plane conductivity of two-dimensional materials is much higher than the out-of-plane conductivity, accelerating electron transport. MXenes is a novel 2D metal carbide and carbonitride of the formula M_n+1X_nT_x(wherein M is an early transition metal, X is C and/or N, and T is a surface functional group). Two-dimensional material Ti₃C₂MXene has the advantages of an open two-dimensional structure, high conductivity, high mechanical property and the like, and is widely applied to the aspects of functional ceramics, photocatalysis, lithium ion batteries, solar batteries, gas sensors and the like. However, in the anode material, due to easy stacking of MXene, the transfer of charges is severely limited by the functional groups (such as-OH, ═ O or-F) carried on the surface, so that the performance thereof cannot be fully exerted.

Tin and tin base materialMaterials are considered ideal anode materials because they have abundant storage capacity, are environmentally friendly and have extremely high theoretical capacity (994mA h g)^-1). However, these materials have problems of poor electron transfer and severe volume expansion during charge and discharge, which in turn limits their application in lithium batteries. In addition, Sn-based materials (e.g., oxides and sulfides of Sn) have poorer theoretical capacity and electron transport capacity than metallic Sn. Therefore, a battery material with excellent electrochemical performance is expected to be obtained by constructing a novel three-dimensional superstructure of MXene and Sn.

Disclosure of Invention

In order to solve the problems, the invention provides Sn @ Ti₃C₂The invention discloses a battery cathode material and a preparation method thereof, and Ti is etched by LiF and HCl₃AlC₂Medium Al layer to obtain Ti₃C₂MXene nanosheets utilizing NaBH₄Reducing the solution to obtain Sn nanoparticles, mixing the Sn nanoparticles with Ti₃C₂Ti prepared from MXene nanosheets₃C₂Mixing and stirring MXene colloidal solution for reaction to finally obtain Sn @ Ti of three-dimensional superstructure₃C₂。

The first purpose of the invention is to provide Sn @ Ti₃C₂A method of preparing a battery anode material, the method comprising the steps of:

(1) preparation of Ti₃C₂MXene nanosheet: mixing Ti₃AlC₂Immersing in mixture of LiF and HCl, stirring to etch Al layer, washing the solid on lower layer after reaction, centrifuging, and dispersing the obtained product in water to obtain Ti₃C₂MXene colloidal solution;

(2) preparing Sn nanoparticles: dissolving tin salt in polyvinylpyrrolidone solution, adding NaBH under vigorous stirring₄Solution, washing, filtering and drying the obtained product after the reaction is finished to obtain Sn nano particles;

(3) preparation of Sn @ Ti₃C₂: mixing Ti in the step (1)₃C₂Slowly adding MXene colloidal solution into the Sn nano-particles in the step (2), continuously and violently stirring, and carrying out reactionAfter the reaction is finished, the obtained mixture is washed, filtered and dried to obtain Sn @ Ti₃C₂。

In one embodiment of the present invention, the Ti in the step (1)₃AlC₂The addition amount of (B) is 0.035-0.05 g/mL.

In one embodiment of the present invention, the concentration of LiF in step (1) is 3 mol/L.

In one embodiment of the present invention, the HCl concentration in step (1) is 9 mol/L.

In one embodiment of the present invention, Ti is added in step (1)₃AlC₂After immersion in a mixture of LiF and HCl, it was stirred for 24h at 35 ℃.

In one embodiment of the present invention, in step (1), the lower layer of solid is washed until the pH value is 6-7.

In one embodiment of the present invention, the Ti in the step (1)₃C₂The concentration of the MXene colloidal solution is 4-6 mg mL^-1。

In one embodiment of the present invention, the tin salt in step (2) is SnCl₂、Sn(NO₃)₂One kind of (1).

In one embodiment of the present invention, the concentration of the polyvinylpyrrolidone solution in the step (2) is 0.45-0.60 mg mL^-1。

In one embodiment of the present invention, the NaBH of step (2)₄The concentration of (b) is 8.0-11 mg mL^-1。

In one embodiment of the present invention, the drying manner in step (2) is drying overnight at 35 ℃ under vacuum.

In one embodiment of the present invention, the Sn nanoparticles and Ti in the step (3)₃C₂MXene is (6-8): 3.

in one embodiment of the present invention, the Sn nanoparticles and Ti in the step (3)₃C₂The mass ratio of MXene is 7: 3.

in one embodiment of the present invention, the continuous vigorous stirring time in the step (3) is 6 to 8 hours.

In one embodiment of the present invention, the drying manner in step (3) is drying overnight at 35 ℃ under vacuum.

The second purpose of the invention is to provide Sn @ Ti prepared by the method₃C₂A battery negative electrode material.

The third purpose of the invention is to provide a lithium ion battery, which comprises the Sn @ Ti₃C₂A battery negative electrode material.

It is a fourth object of the present invention to provide the above Sn @ Ti₃C₂The battery cathode material is applied to the fields of portable electronic products and smart power grids.

The invention has the beneficial effects that:

(1) sn @ Ti prepared by the invention₃C₂The Sn nano particles can be effectively embedded into Ti₃C₂In MXene nano-sheet, Sn @ Ti of three-dimensional superstructure is presented through self-assembly₃C₂(ii) a With Ti₃C₂Compared with MXene, Sn @ Ti in layer-by-layer superstructure₃C₂Has a significantly increased specific surface area of Sn @ Ti₃C₂Specific Surface Area (SSA) value of 14.868m²Higher specific surface area can provide more active sites, which is advantageous for electron and ion transport.

(2) Sn @ Ti with 3-dimensional superstructure formed by self-assembly in the invention₃C₂Has good stability and excellent electrochemical reversibility, and is 0.5A g^-1After 100 cycles, the lithium removal capacity is 577mA h g^-1，Sn@Ti₃C₂The initial CE (coulombic efficiency) of (1) was 67.46%, gradually increased and stabilized above 97%; sn @ Ti₃C₂At 3A g^-1After being subjected to a high current density, Sn @ Ti₃C₂The lithium removal specific capacitance of the electrode is reduced back to 0.1Ag at the current density^-1Then the temperature is immediately recovered to 686mA h g^-1After 100 cycles, Sn @ Ti₃C₂The specific capacity of the material can be still maintained at 702.38mAh g^-1And good reversibility is shown.

Drawings

SEM and TEM images of the sample of fig. 1; wherein FIG. 1(a-b) shows Ti before and after LiF/HCl etching₃AlC₂FIG. 1(c) is an SEM image of Sn nanoparticles, and FIG. 1(d-e) is Sn @ Ti₃C₂FIG. 1(f) is a view of Ti after LiF/HCl etching₃AlC₂TEM of (1 (g-h) is Sn @ Ti₃C₂A TEM image of (a).

The XRD pattern of the sample of fig. 2; wherein FIG. 2(a) is Ti₃AlC₂And Ti₃C₂XRD pattern of (A), FIG. 2(b) shows Sn nanoparticles and Ti₃C₂And Sn @ Ti₃C₂XRD pattern of (A), FIG. 2(c) shows Sn nanoparticles and Ti₃C₂And Sn @ Ti₃C₂N of (A)₂Adsorption/desorption isotherms.

FIG. 3 shows Sn, Ti₃C₂And Sn @ Ti₃C₂Nyquist plot for the electrode.

FIG. 4 is Sn @ Ti₃C₂At 0.5Ag^-1Next, galvanostatic discharge-charge curves for

cycles

1, 2, 5, 50 and 100.

FIG. 5 shows Sn nanoparticles, Ti₃C₂MXene nanosheet and Sn @ Ti₃C₂Lithiation specific capacity curve of (a).

FIG. 6 is Sn @ Ti₃C₂And (3) a cyclic discharge curve diagram of the electrode under different multiplying current.

Fig. 7 is a picture of Sn nanoparticles with PVP (right) and without PVP (left) after 30min of synthesis.

Fig. 8 is an SEM image of Sn nanoparticles with PVP (right) and without PVP (left).

FIG. 9 is Sn @ Ti of comparative example 2₃C₂A map of electrochemical performance of; wherein, FIG. 9(a) is Sn @ Ti₃C₂Lithiation specific capacity curve of (a); FIG. 9(b) is Sn @ Ti₃C₂And (3) a cyclic discharge curve diagram of the electrode under different multiplying current.

Detailed Description

The present invention is described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited to these examples.

Example 1

(1) Preparation of Ti₃C₂MXene nanosheet: 0.5g of Ti₃AlC₂The Al layer was etched by immersing in 10mL of a mixture of 3M LiF and 9M HCl and stirring at 35 ℃ for 24 h. After the reaction is finished, washing the acidic mixture with deionized water for the lower-layer solid, centrifuging until the pH value is 6-7, and finally dispersing the obtained sample in the deionized water to form Ti₃C₂MXene colloidal solution with concentration of 5mg mL^-1；

(2) Preparing Sn nanoparticles: 200mg of SnCl₂0.5mg mL dissolved in 20mL^-1Then 5mL of 10mg mL are added under vigorous stirring^-1NaBH₄The solution was slowly added to the above mixture. Washing the obtained sample with deionized water, filtering, and drying at 35 ℃ under vacuum overnight to obtain Sn nanoparticles;

(3) preparation of Sn @ Ti₃C₂: mixing 10mL of Ti in the step (1)₃C₂Colloid (Ti)₃C₂) Slowly adding the solution into the Sn nano particles in the step (2), and arranging the Sn nano particles and Ti₃C₂The mass ratio of MXene is 7: 3. continuously and vigorously stirring for 6h, washing the mixture obtained after the reaction is finished with deionized water, and filtering to obtain Sn @ Ti with a three-dimensional structure₃C₂And dried in vacuo at 35 ℃ overnight to give Sn @ Ti₃C₂。

Example 2 characterization test

The sample microscopic morphology and structure can be observed by Scanning Electron Microscopy (SEM). FIG. 1(a-b) shows Ti before and after LiF/HCl etching₃AlC₂As can be seen from the SEM image of fig. 1(b), the Al layer is completely etched away, and the overall layered structure is present. Fig. 1(c) is an SEM image of Sn nanoparticles, and as can be seen from fig. 1(c), the average size of the prepared Sn nanoparticles was 50 nm. As shown in FIG. 1(d-e), Sn nanoparticles can be efficiently embedded in Ti₃C₂In MXene nano-sheet, Sn @ Ti of three-dimensional superstructure is presented through self-assembly₃C₂。

The microstructure can be further studied by Transmission Electron Microscopy (TEM). The TEM image of FIG. 1(f) shows that Ti₃C₂Consisting of a layered structure after etching the Al layer, which is consistent with the results obtained by SEM. As shown in FIG. 1(g), a single Ti₃C₂MXene nanoplatelets have a thickness of about 1.2nm and a lattice spacing value of about 0.236nm, which is comparable to the previously reported Ti₃C₂The case of MXene nanoplatelets is essentially the same. FIG. 1(h) is Sn @ Ti₃C₂Can also be seen in the TEM image of₃C₂The layer-by-layer assembly of (A) represents Sn @ Ti of a three-dimensional superstructure₃C₂This is also consistent with the results obtained from the SEM images above.

The structure and phase of the sample can be observed by X-ray diffraction (XRD) patterns. FIG. 2(a) is Ti₃AlC₂And Ti₃C₂XRD pattern of (1), and by comparison, Ti was found after etching₃C₂The crystallinity and structural order of MXene nanoplatelets are significantly lost and these results are consistent with fig. 1 (b). Furthermore, the shift of the (002) peak to a lower angle indicates Ti after the Al layer is etched₃C₂The MXene interlamellar spacing becomes smaller. In FIG. 2(b), we observed the use of NaBH₄All peaks in the Sn nanoparticles prepared by the reduction method are consistent with the spectrogram card number (JCPDS card number: 86-2264), namely Sn @ Ti₃C₂In XRD pattern of (A), Ti₃C₂And the appearance of peaks (200), (101), (220), (211), (200), (112) and (400), (321) of the Sn nanoparticles, indicating Ti₃C₂And the structure of the Sn nanoparticles is not changed. Obtained N₂The adsorption/desorption isotherm samples are shown in fig. 2 (c). At P/P₀0.4-1.0 (relative pressure), Ti₃C₂Sn and Sn @ Ti₃C₂Exhibit a mesoporous structure. Furthermore, by the Barret-Joyner-Halenda (BJH) method, we observed Ti₃C₂Sn and Sn @ Ti₃C₂Have Specific Surface Area (SSA) values of 4.893, 11.024 and 14.868m, respectively²(ii) in terms of/g. With Ti₃C₂Compared with MXene, Sn @ Ti in layer-by-layer superstructure₃C₂The specific surface area of (2) is remarkably increased. Higher ratio tableThe area can provide more active sites, which is advantageous for electron and ion transport.

Example 3 electrochemical testing

The prepared active material is prepared into a CR2016 type button battery, a lithium sheet is used as a negative electrode, and the obtained samples (Sn, Ti) are subjected to electrochemical reaction₃C₂，Sn@Ti₃C₂) An electrochemical measurement is performed. A slurry of active material was prepared by mixing the active material, carbon nanotubes and PVDF (weight ratio 7:1.5:1.5) in N-methyl-2-pyrrolidone, and the electrolyte was LiPF dispersed in a mixture of ethylene carbonate and diethyl carbonate (volume ratio 1: 1)₆(1M), and the battery diaphragm is a polypropylene film (Celgard-2300). Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were measured on the CHI660D electrochemical workstation, and galvanostatic charge/discharge measurements were performed on a Neware battery test system.

FIG. 3 shows Sn, Ti₃C₂And Sn @ Ti₃C₂Nyquist plot for the electrode. From FIG. 2, Sn, Ti can be seen₃C₂And Sn @ Ti₃C₂The nyquist plots for the electrodes all have similar characteristics: the high frequency is a semicircle, and the low frequency is a straight line. In the nyquist diagram, a semicircle sinking at a high frequency corresponds to a charge transfer resistance (Rct), and a tilted line at a low frequency is Warburg resistance (Ws) in which lithium ions are diffused in an electrode. Apparently, Sn @ Ti of the three-dimensional superstructure₃C₂The Rct of the electrode is much lower than that of a pure Sn nanoparticle electrode, which demonstrates that Ti₃C₂MXene has obvious positive effect on increasing electronic and ionic conductivity in electrode, and Ti₃C₂MXene can effectively improve Sn @ Ti₃C₂Electron and ion transport.

FIG. 4 shows that the pressure at 0.5A g^-1Sn @ Ti in the following 1, 2, 5, 50 and 100 th cycles₃C₂Typical constant current discharge-charge behavior. As can be seen from FIG. 4, Sn @ Ti₃C₂The charge capacity of the electrode in the initial cycle was 701mA hr g^-1The discharge capacity is 1039mA h g^-1The calculated Coulombic Efficiency (CE) was 67.46%. Sn @ Ti₃C₂Initial irreversible capacity of electrodeThe amount decreased, indicating that an SEI film was formed. In the second cycle, Sn @ Ti₃C₂The delithiation and lithiation capacities of (1) were estimated to be 653 and 756mA h g^-1And its CE was 86.37% higher than the initial CE. The plateau of the charge-discharge curve after long cycling remained essentially unchanged by comparison, indicating that Sn @ Ti₃C₂The structure of (2) is less damaged in the charging and discharging process.

FIG. 5 shows Sn nanoparticles, Ti₃C₂MXene nanosheet and Sn @ Ti₃C₂Lithiation specific capacity curve of (a). Sn @ Ti with 3D superstructure formed by self-assembly₃C₂Has good stability and excellent electrochemical reversibility, and is 0.5A g^-1After 100 cycles, the lithium removal capacity is 577mA h g^-1. Furthermore, Sn @ Ti₃C₂The initial CE of (a) was 67.46%, gradually increasing and stabilized above 97%. In contrast, after 100 cycles, Ti₃C₂The reversible capacity of MXene electrode was about 145mA hg^-1This value is much lower than Sn @ Ti₃C₂The charge and discharge capacity of (1). In addition, the capacity of Sn nanoparticles decreases rapidly due to severe volume expansion. Thus, Sn @ Ti₃C₂The electrode shows excellent electrochemical cycle performance and higher reversible capacity, which is attributed to Sn @ Ti of 3-dimensional superstructure₃C₂Laminated by self-assembled layers.

FIG. 6 is Sn @ Ti₃C₂And (3) a cyclic discharge curve diagram of the electrode under different multiplying current. As can be seen from FIG. 6, Sn @ Ti increases with the current density₃C₂The capacity of the electrodes is gradually decreasing. Sn @ Ti₃C₂At 0.1, 0.3, 0.5, 1 and 3A g^-1The average discharge capacities at this time were 803, 633, 562, 453 and 238mA h g, respectively^-1。Sn@Ti₃C₂At 3A g^-1After being subjected to a high current density, Sn @ Ti₃C₂The specific lithium removal capacity of the electrode decreased back to 0.1A g at the current density^-1Then the temperature is immediately recovered to 686mA h g^-1. More importantly, Sn @ Ti after 100 cycles₃C₂The specific capacity of the catalyst can still be maintained at 702.38mA h g^-1Thereby exhibiting good reversibility.

Comparative example 1

(1) Preparation of Ti₃C₂MXene nanosheet: same as in step (1) in example 1;

(2) preparing Sn nanoparticles: the same procedure as in (2) of example 1 was repeated except that no surfactant, polyvinylpyrrolidone PVP, was added;

(3) preparation of Sn @ Ti₃C₂: same as in step (3) in example 1.

(4) Characterization test:

fig. 7 is a picture of Sn nanoparticles with PVP (right) and without PVP (left) after 30min of synthesis. As can be seen from fig. 7, the Sn nanoparticles prepared by the surfactant PVP-assisted method are uniformly dispersed in water, so that the aqueous solution is opaque, and the opposite is true for the Sn nanoparticle solution with PVP value of 0. In fig. 1(c) and fig. 8, we can observe that the average size of Sn nanoparticles with PVP is 50nm, significantly smaller than the average size of Sn nanoparticles without PVP added. Therefore, the surfactant-assisted method can effectively control the synthesis size of tin nanoparticles.

Comparative example 2

(1) Preparation of Ti₃C₂MXene nanosheet: same as in step (1) in example 1;

(2) preparing Sn nanoparticles: same as step (2) in example 1;

(3) preparation of Sn @ Ti₃C₂: providing Sn nanoparticles and Ti₃C₂The mass ratio of MXene is 3: 7, the rest was the same as in the step (3) of example 1, to obtain Sn @ Ti₃C₂。

(4) Test results of electrochemical Properties

FIG. 9 is Sn @ Ti of comparative example 2₃C₂A map of electrochemical performance of; wherein, FIG. 9(a) is Sn @ Ti₃C₂Lithiation specific capacity curve of (a); FIG. 9(b) Sn @ Ti₃C₂And (3) a cyclic discharge curve diagram of the electrode under different multiplying current. By comparison with FIG. 9 (Sn/Ti)₃C₂3/7), the comparison of Sn/Ti in example 1 can be found₃C₂Sn @ Ti of 7/3₃C₂Has higher charge-discharge capacity and better rate stability.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. Sn @ Ti₃C₂The preparation method of the battery negative electrode material is characterized by comprising the following steps:

(3) preparation of Sn @ Ti₃C₂: mixing Ti in the step (1)₃C₂Slowly adding MXene colloidal solution into the Sn nano-particles in the step (2), continuously and violently stirring, washing a mixture obtained after the reaction is finished, filtering and drying to obtain Sn @ Ti₃C₂。

2. The method of claim 1, wherein the Ti in step (1)₃C₂The concentration of MXene colloidal solution was 4mg mL^-1～6mg mL^-1。

3. The method according to claim 1, wherein the tin salt in step (2) is SnCl₂、Sn(NO₃)₂One kind of (1).

4. The method according to claim 1, wherein the concentration of the polyvinylpyrrolidone solution in the step (2) is 0.45-0.60 mg mL^-1。

5. The method of claim 1, wherein the NaBH in step (2)₄The concentration of (A) is 8.0 to 11mgmL^-1。

6. The method of claim 1, wherein the Sn nanoparticles and Ti in step (3)₃C₂MXene is (6-8): 3.

7. the method of claim 1, wherein the Sn nanoparticles and Ti in step (3)₃C₂The mass ratio of MXene is 7: 3.

8. sn @ Ti prepared by the method of any one of claims 1 to 7₃C₂A battery negative electrode material.

9. A lithium ion battery, characterized in that the lithium ion battery comprises Sn @ Ti of claim 8₃C₂A battery negative electrode material.

10. Sn @ Ti as claimed in claim 8₃C₂The battery cathode material is applied to the fields of portable electronic products and smart power grids.